In their natural environment, bacteria are exposed to various stresses. The stress-response sigma factor SigB of gram-positive Bacillus subtilis is the best-characterized example. Unlike Bacillus subtilis, the gram-positive bacterium Streptomyces coelicolor A3(2) contains nine SigB homologues (SigBFGHIKLMN) with a major role in differentiation and response to osmotic stress. We previously constructed a two-plasmid system to identify promoters recognized by these sigma factors. Interestingly, almost all identified promoters were recognized by two or more SigB homologues. However, no specific sequences characteristic for these recognition groups were found. To examine this cross-recognition in vivo in S. coelicolor A3 (2), one of these promoters was cho-sen, which drives the expression of the sporulation-specific gene ssgB. The ssgBp promoter was inserted into a luciferase reporter plasmid and conjugated to S. coelicolor M145 and nine mutant strains containing deleted individual sigB homologous genes. Luciferase reporter activity indi-cated differential activity of this promoter in these mutant strains, suggesting overlapping pro-moter recognition by these SigB homologues. To determine which nucleotides in the ̶ 10 re-gion are responsible for the selection of a specific SigB homologue, several mutant promoters with altered last three nucleotides in this region were prepared and tested in the two-plasmid system. Some mutant promoters were specifically recognized by some SigB homologues. Mutant promoters were inserted into a luciferase reporter plasmid and conjugated to S. coelicolor A3(2) and these nine mutant strains. Luciferase reporter activity indicated differential activity of these ssgBp mutant promoters, indicating overlapping promoter recognition by these SigB homologues in S. coelicolor A3(2).